ARIA (Accessibility/Remoteness Index of Australia).

ARIA+ is widely accepted as Australia's most authoritative geographic measure of remoteness.

ARIA and its successors ARIA+ and ARIA++, are indexes of remoteness derived from measures of road distances between populated localities and Service Centres. These road distance measures are then used to generate a remoteness score for any location in Australia.

What is ARIA?

ARIA+, like its predecessor ARIA, is an unambiguously geographical approach to defining remoteness. ARIA+ is a continuous varying index with values ranging from 0 (high accessibility) to 15 (high remoteness), based on road distance measurements from over 12,000 populated localities to the nearest Service Centres in five categories based on population size. The five distance measurements, one to each level of Service Centre, is recorded for each populated locality and standardized to a ratio. The ratio is calculated by dividing the measured distance for a given locality by the Australian average (mean) for that category. After applying a threshold of three to each of the ratios, all ratios are summed to produce the ARIA+ score for each populated locality across Australia.

An interpolation procedure is then used to derive the index values for each of the localities to a 1 km grid so that all areas of Australia are able to be assigned an index value. Using the interpolated grid surface, scores for larger areas such as SA1, SA2, LGAs, etc.., can be derived.

The major advantages of ARIA over other methods of measuring remoteness are;

it is a purely geographic measure of remoteness, which excludes any consideration of socio-economic status, 'rurality' and populations size factors (other than the use of breaks in the population distribution of Urban Centres to define the Service Centre categories);

it is flexible and can be aggregated to a range of spatial units, used as a continuum or classified;

its methodology is conceptually clear;

it is precise; and

it is relatively stable over time.

As a comparable index of remoteness that covers the whole of Australia, ARIA provides a measure of remoteness that is suitable for a broad range of applications including assisting in service planning, demographic analysis and resource allocation.

Although ARIA+ provides a measure of accessibility and remoteness for the whole of Australia, including metropolitan and non-metropolitan areas, the principal focus of the index has been to quantify accessibility in non-metropolitan Australia. This is not to deny the importance of service access issues within major urban areas, but a detailed analysis of accessibility within urban areas is believed better served by a dedicated methodology - Metro ARIA.

Brief Methodology

Terminology

ARIA+ - (Accessibility/Remoteness Index of Australia Plus) measures remoteness in terms of access along the road network from populated localities to each of five categories of Service Centre. Localities that are more remote have less access to Service Centres; those that are less remote have greater access to Service Centres.

Populated Localities - these are based on AUSLIGs (now Geoscience Australia) ‘Populated Centres' and supplemented with some additional populated towns from the AUSLIG gazetteer and other mapping sources. Localities were only added to the database if they were known to be populated. There are over 12,000 populated localities in the 2011 ARIA+ database.

If one thinks of ARIA as based on the distances people have to travel to obtain services, then populated localities are where they are coming from, and Service Centres are where they are going to.

Service Centres - are populated localities where the population is greater than 1,000 persons (greater than 200 in the case of ARIA++). The Urban Centre/Locality structure from the Australian Bureau of Statistics (ABS) has been used to define the extent and population of these areas.

The table below shows the population break points that were used to group Urban Centres into the five Service Centre categories. The ARIA+ analysis considers over 700 Services Centres in determining remoteness values across Australia. These Service Centres are a subset of the 12,000+ populated localities.

In instances where the ABS defined Urban Centres are split by a state border, such as in the case of Albury and Wodonga, the population and spatial extents for each of these Urban Centres have been combined and treated as one Service Centre.

Service Centre Category

Urban Centre Population

A

250,000 persons or more

B

48,000 - 249,999 persons

C

18,000 - 47,999 persons

D

5,000 - 17,999 persons

E

1,000 - 4,999 persons

F (ARIA++ only)

200 - 999 persons

Index Derivation

The ARIA+ methodology regards services as concentrated into Service Centres. Populated localities with populations of greater than 1,000 persons are considered to contain at least some basic level of services (for example health, education, or retail), and as such these towns and localities are regarded as Service Centres. Those Service Centres with larger populations are assumed to contain a greater level of service provision.

The road distance from each of the 12,000+ populated localities to the boundary of the nearest Service Centre in each category was calculated. This calculation resulted in five distance measurements being recorded for each populated locality, one for each Service Centre. Populated towns within a Service Centre (based on ABS-defined Urban Centre boundaries) in the relevant category were given a distance value of zero for that category. Each distance value was divided by the Australian average (mean) for that category in order to derive a standardised (or ratio) value. Distance measurements are standardised so that large distance measurements would not overwhelm the effect of the other distance measurements.

Each ratio value is thresholded at three (i.e. three times the Australian mean) to remove the effects of any remaining extreme values from the index. All towns with a ratio value higher than three for a given category are considered 'remote' in terms of access to that category, and were given a value for that category equal to the threshold. For each populated locality, the standardized value from each of the five Service Centre categories is summed to produce an overall index value ranging between 0 and 15. The lower the value, the greater the access to services

Example ARIA+ Calculation

The example below shows how the ARIA+ 2011 score for Pine Creek is calculated (Please note: rounding has been applied for the purpose of this example).

* There were no Category C Service Centres closer to Pine Creek than Darwin, so Darwin functions as both the closest Class B and Class C centre. ** There were no Category E Service Centres closer to Pine Creek than Katherine, so Katherine functions as both the closest Class D and Class E centre

Interpolating ARIA Scores to Generate a Continuous Remoteness Surface

The ARIA values for all populated localities are then spatially interpolated to form a grid of 1km cells across the whole of Australia. This grid enabled remoteness to be expressed continuously over the total land area. In addition, it allows ARIA values to be calculated (by summation of 1km grid cells) for any statistical geography, including SA1's, Statistical Local Areas, and Local Government Areas.

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